1. Field of Invention
The present invention relates generally to internal combustion engines and, more specifically, to a method for detecting detonation phenomena in an internal combustion engine.
2. Description of Related Art
Spark ignited internal combustion engines typically include a plurality of cylinders, each of which has a piston that cyclically slides within the cylinder. Each cylinder also includes a spark plug that is cyclically operated by an electronic control unit to generate a spark between its electrodes, and thus determine the ignition of the compressed gases within the cylinder itself. The control unit includes a memory, in which a series of maps which provide the operating values of the spark plugs as a function of the current engine point; in particular, the maps provide the value of the spark advance for each spark plug (the value of the angular interval existing between the ignition; the generation of the spark between the electrodes of the spark plug) and the top dead center or TDC of the piston. If the value of the spark advance is zero, then the ignition (the generation of the spark between the electrodes of the spark plug) occurs exactly at the top dead center or TDC of the piston.
The values of the spark advance stored in the maps contained in the control unit are determined during the engine set up phase to attempt to ensure a good combustion under all possible conditions of operation and obtain a good thermal efficiency of the engine while safeguarding the integrity of the engine itself (avoiding the presence of excessive detonation phenomena in the cylinders). Detonation is an explosive type of combustion of the air-fuel mixture, which occurs before the mixture is reached by the flame front generated by the spark plug. A series of pressure waves are created upon the detonation, which cross the combustion chamber and violently impact against the metal walls. Detonation occurs when given critical temperature and pressure values are exceeded inside the chamber (which may vary even considerably from engine to engine) and which, when occurring at medium-to-low rpm, often cause a typical (and clearly perceivable) metallic noise known as “knocking” or “pinging”.
Detonation normally occurs when spark advance is excessive, when a fuel with an excessively low octane rating is used (the antiknock potential of a fuel is indeed indicated by its octane rating) or, for supercharged/turbocharged engines, when the boost pressure is too high. The combustion trend is influenced by many factors (the most important are the fuel features, the engine head temperature, and the spark plug decay), the effect of which is significantly difficult to predict with accuracy. Thus, the absence of excessive detonation is detected and, in the case of excessive detonation in a cylinder, the control unit reduces the value of the spark advance for the cylinder so as to eliminate the detonation in the cylinder itself (so that the maximum pressure reached in the cylinder is reduced and occurs later with respect to TDC, making the detonation event “less likely”). However, in terms of combustion efficiency, reducing the spark advance of a cylinder corresponds to a loss of thermodynamic efficiency; the air mass for the cylinder (and, thus, the injected gasoline mass) is maintained constant. However, by reducing the spark advance, the combustion efficiency (the fraction of chemical energy which is converted into mechanical energy) is reduced, resulting in negative repercussions on fuel consumption and the generation of polluting substances (emissions).
Thus, there remains a need in the art for a strategy for effectively recognizing the development of excessive detonation.